<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .erweima {
        height: 100px;
        width: 100px;
        background-color: skyblue;
      }
      .hide {
        display: none;
      }
      .show {
        display: block;
      }
    </style>
  </head>
  <body>
    <div class="erweima hide" id="er"></div>
    <script>
      var div = document.getElementById('er')
      div.className = div.className.replace('hide', 'show')
    </script>
  </body>
</html>
